The present invention is directed to fractionation columns and, more particularly, to fractionation trays having manways.
Fractionation trays are used in fractionation columns to facilitate contact and interaction between ascending vapor streams and descending liquid streams. A plurality of fractionation trays are normally installed in a vertically spaced apart relationship within the column. Each tray typically extends horizontally across the entire cross-section of the column and is supported by rings or other supports welded to the inner surface of the column shell.
Fractionation trays are frequently provided with manways that can be opened to provided a temporary vertical passageway through the trays once they have been installed within the column. The manways are typically formed by an opening in each tray deck and an overlying cover formed by one or more removable panels. When internal access to the column is needed for inspection, cleaning, and/or maintenance purposes the manway covers are removed from the trays and a person is able to pass vertically through the trays and the column.
One manway cover, that remains in widespread use, utilizes numerous bolting assemblies to releaseably secure the manway cover to the overlapped edges of the surrounding tray panels. The bolting assemblies typically include a rectangularly shaped flat washer that is positioned on a vertical bolt that passes through the overlapped portions of the manway cover and apertures within the tray panels. Nuts are subsequently threaded on the opposite ends of the bolts and tightened to secure the cover to the surrounding tray panels.
While this manway and cover design is simple to use and reliable, opening and closing of the manway cover is a time consuming process as each bolting assembly of the respective manway needs to be tightened or loosened before the manway cover is opened or closed. This problem is compounded due to the large number of fractionation trays contained within any given column.
Manway designs which facilitate quicker opening and closing than those discussed above are disclosed in U.S. Pat. Nos. 4,120,919 and 6,629,687. The manway disclosed in the '919 patent utilizes a cover formed from two panels that are joined together by a center hinge. The lateral margins of the panels are releaseably secured beneath clips that are welded or otherwise secured to the edges of the adjacent tray panels. The ends of the cover are releaseably secured to the adjacent end panels by a handle arrangement. When removal of the manway cover is desired, the handles are turned to release the cover from the end panels and the center hinge allows the cover panels to be folded upwardly, thereby releasing the lateral margins of the panels from the clips and the entire manway cover can be removed from the fractionation tray.
The manway disclosed in the '687 patent likewise utilizes a cover formed from two panels that are joined together by a center hinge. The lateral margins of the cover panels have upturned flanges that are releaseably secured beneath U-shaped brackets affixed to the fractionation tray deck adjacent the manway opening. Each of the U-shaped brackets are bolted, via a pair of bolting assemblies, to the edges of the adjacent fractionation tray panels. When the cover is opened the upturned flanges of the cover panels slide out of the U-shaped brackets bolted to the fractionation tray and the entire manway cover can be removed from the fractionation tray.
While the manway designs described in the '919 and '687 patents allow for quicker opening and closing of the manway covers, additional hardware must be provided and modifications must be made to the adjacent fractionation tray panels in order to install the manway covers (e.g. welding or bolting of brackets/clips to the fractionation tray). In addition, folding of the center hinge during removal of the cover in the '919 patent initially causes a slight outward movement of the cover panels and may cause them to become tightly wedged and difficult to remove from beneath the clips. Furthermore, both manway designs require complete removal of the manway cover from the fractionation tray when they are opened and thus require subsequent realignment of the manway panel with the manway opening and brackets/clips when closing. This adds additional time requirements when utilizing these manways. Manways for fractionation trays and columns which overcome these problems, among others, are therefore desired.